The present invention generally relates to image processings and more particularly to a parallel optical image processing system having an associative memory function.
Conventionally, application of parallel optical image processing is studied in various filterings and correlation evaluations. This technique is based on the analog Fourier transform using a single lens and has an extremely high processing speed. On the other hand, it has a problem in the accuracy and reliability because of the limitation pertinent to the nature of analog processing. Thus, at the moment, image processing is performed mainly on the basis of digital processing using digital computer which is easy to be programmed and can perform various processing functions. However, the digital processing is a time sequential procedure and needs substantial processing time as well as substantial memory space when applied to the processing of images.
On the other hand, there is a proposal to combine digital computer and optical processing as is disclosed in the Japanese Laid-open Patent Application No.61-179424. In this system, an optical logic operation is performed by using a two dimensional optical memory array and an optical interconnection array confronting the optical memory array. The optical interconnection array changes the optical path of the optical beam incident thereto and the system performs logical operation such as addition, subtraction, multiplication or division of the input image information. This system, however, has no associative memory function.
Further, there is proposed an optical parallel image processing system having an associative memory function in which a complete image is obtained on the basis of an incomplete input image. For example, there is described a feedback optical processing system using a hologram memory and a threshold device for obtaining a complete image on the basis of incomplete input image (Abu-Mostafa et al. "Optical Neural Computers", Scientific American Vol.256, Number 3, pp.66-73, 1987).
Further, there is an optical parallel image processing system as disclosed in the Japanese Laid-open Patent Application No.62-106590 or No.58-22147 in which pattern recognition or segmentation of a number of patterns is performed by a neural network model. This conventional system allows parallel displacement of input image and has a capability of operating as an associative memory. However, the system has a problem in that it has to have an optical system which is constructed with extreme precision because of the reason that the system handles fully analog images. In other words, such a system is fragile and the recalled image tends to be deteriorated. Further, the system has a problem in that further processing of the obtained image by digital computer is difficult.
Meanwhile, various optical devices are proposed in the field of optical telecommunications for modulation and deflection of optical beams. Such optical devices have no moving parts and performs the polarization of light beam or deflection of the light beam. Some of such devices are already in use in the apparatus such as optical printers for modulating the intensity of the beam. Further, logic devices using such an optical device is also proposed. However, there is no optical device which performs such modulation and deflection of the optical beam and at the same time designed in a form convenient for application to the optical image processing system having associative memory function. In a typical example disclosed in the Japanese Laid-open Patent Application No.63-26636, the optical device is constructed in a form of wave guide in which one of the output beams has a strong optical power when a control signal is supplied while the other of the output beams has the strong optical power when the control signal is not supplied. Obviously, such a device having the wave guide structure is difficult to construct in a form of two-dimensional matrix which is suited for the parallel optical processing system.
In summary, there is no known parallel optical image processing system for performing an associative memory function wherein the system has a flexibility in the optical interconnection between the optical elements in the system in addition to the ability of the optical parallel processing.